Method and apparatus for controlling multiple beam spacing

ABSTRACT

An anamorphic optical element and an adjustment mechanism for selectively rotating the optical element either around an axis substantially in a vertical direction, an axis substantially in an optical axis direction, an axis substantially in a plane formed by the vertical direction and the optical axis direction, or combination of axes thereof is used to vary a vertical separation between two or more spots.

BACKGROUND

Recent improvements in printing have concentrated on increasing thespeed of printing pages. In an electrophotographic printer, multiplelight beams from a light emitter array may be used to increase printspeed by forming swaths of scan lines. If the scan lines in a swath arenot properly spaced, banding occurs. Banding lowers print quality.

The spacing of the scan lines is precisely aligned in an exposure moduleof the printer that is sent to the user. The module may be shipped withthe printer. The module may become misaligned in shipping, printersetup, printer operation, and the like. The misalignment may be due totemperature variations, vibration, pressure, or other factors. If theprinter exhibits banding, the module is removed from the printer andsent to a laboratory especially equipped for precisely aligning theexposure module. Removing and realigning the module is costly. The actof realigning the exposure module may not eliminate, nor minimize, norguarantee the future absence of banding. When the exposure module isremoved, the printer may be unavailable for use.

Therefore, there is a need for adjusting scan line spacing inelectrophotographic printers which have multiple light beams. There isalso a need to avoid the costly process of removing and realigning theexposure module. Furthermore, there is a need to improve theavailability of the printer for use.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments for an optical adjustment of a multibeam system can bebetter understood with reference to the following drawings which show anembodiment of a printing system. The elements of the drawings may not beto scale relative to each other. Rather, emphasis has been placed uponclearly illustrating the embodiments of the multibeam adjustment in aprinter. Certain dimensions have been exaggerated in relation to otherdimensions for clarity and better understanding of this disclosure.Furthermore, like reference numerals designate corresponding similarparts through the several views.

FIG. 1 shows a cross sectional view of a light emitter array accordingto an embodiment of an electrophotographic printing system.

FIG. 2 a illustrates a cross sectional diagram of a portion of anoptical system, including the light emitter array of FIG. 1 according toan embodiment of an electrophotographic printing system.

FIG. 2 b illustrates an enlarged view of the light emitter array of anoptical system shown in FIG. 2 a.

FIG. 3 shows a perspective view of an optical system according to anembodiment of an electrophotographic printing system.

FIG. 4 shows swaths of scan lines which are correctly aligned accordingto an embodiment of an electrophotographic printing system.

FIG. 5 illustrates swaths of scan lines which are spaced apart accordingto an embodiment of an electrophotographic printing system.

FIG. 6 shows swaths of scan lines which are narrowly spaced according toan embodiment of an electrophotographic printing system.

FIG. 7 shows scan lines illumating an optical sensor and the spatialdistribution of light according to an embodiment of anelectrophotographic printing system.

FIG. 8 shows an embodiment of an adjustment mechanism for rotatingoptical elements around a vertical axis according to an embodiment of anelectrophotographic printing system.

FIG. 9 is a graph of scan line vertical separation as a function of anangle of two prisms rotated around a vertical axis according to anembodiment of an electrophotographic printing system.

FIG. 10 is a graph of the percent change in the distance between twoscan lines as a function of an angle of two prisms rotated around avertical axis according to an embodiment of an electrophotographicprinting system.

FIG. 11 illustrates another embodiment of an adjustment mechanism forrotating optical elements about an optical axis direction according toan embodiment of an electrophotographic printing system.

FIG. 12 is a graph of scan line vertical separation as a function of twoprisms rotated around the optical axis according to an embodiment of anelectrophotographic printing system.

FIG. 13 is a graph of the percent change in the distance between twoscan lines as a function of an angle of two prisms rotated around anoptical axis according to an embodiment of an electrophotographicprinting system.

FIG. 14 illustrates an electrophotographic printing system according toan embodiment of an electrophotographic printing system.

FIG. 15 shows a flow diagram having procedural acts according to anembodiment of an electrophotographic printing system.

DESCRIPTION

Electrophotographic printers can use multiple light beams from a lightemitter array to increase printing speed. Rather than scanning one beamacross a photosensitive medium to form one scan line, two or more beamsmay be scanned concurrently to produce two or more scan lines in animage. The intensity of each beam may be independently modulated torender an image.

Each group of scan lines exposed by a group of light beams emitted by alight emitter array forms a swath of scan lines. If the height of aswath is correct, successive swaths are properly spaced and there islittle line-to-line spacing variation in the image. However, if theheight of a swath is large, the space between adjacent swaths becomesnarrow. In printed output, dark scan lines on a light background mayappear to have an anomalously dark band between adjacent swaths. Thisline-to-line variation in perceived print density is a form of banding.Furthermore, if the height of a swath is small, the space betweenadjacent swaths becomes wide. Dark scan lines printed on a lightbackground may then appear to have an anomalously light band betweenadjacent swaths. This line-to-line variation is also a form of banding.

To reduce banding, the light emitter array may be adjusted. For example,the light emitter array may be rotated such that there is littleline-to-line spacing variation within a swath and between swaths.However, the swath height is sensitive to rotations of the light emitterarray. This sensitivity is such, that, to achieve correct swathalignment, it is often necessary to precisely rotate the light emitterarray in a specially equipped laboratory.

As described herein—in an embodiment of an electrophotographic printingsystem—one or more optical elements in the optical path are rotated. Theone or more optical elements may be, but are not limited to, prisms. Therotation may be around an optical axis, a vertical axis, or an axis inthe plane of the optical axis and the vertical axis. The rotationadjusts a vertical spacing of the light emitter array and therebyadjusts scan line spacing. The rotation of one or more prisms around oneor more of these axes results in less sensitivity of beam spacing toadjustment in angle than by rotating the light emitter array. Thisreduction in sensitivity is desirable. The reduction in sensitivityallows the swath height to be adjusted at a site where the printer isused without the inconvenience and cost of removing the exposure modulefrom the printer and sending it to a possibly distant facility foradjustment. Furthermore, the change in beam spacing is substantiallylinear with prism rotation, making automatic control of swath heightstable and predictable.

Embodiments which describe beam height adjustment are described inreference to the following figures:

FIG. 1 shows a light emitter array 102 according to an embodiment of anelectrophotographic printing system. The light emitter array 102 may beformed from light sources 110. As an example, the light emitter array102 may be formed from individual light sources 110A through 110Lstacked together or fabricated in proximity to each other. Regardless,the light emitter array 102 is not limited to these types of devices.Twelve light sources 110A through 110L are shown; although, there may bemore or less than twelve light sources. The light emitter array 102 maybe formed from light sources 110 which are laser diodes. The laserdiodes may be elements of an edge-emitting laser array formed from asingle epitaxial structure; they may also be elements of a one or twodimensional vertical cavity surface emitting laser array (VCSEL), avertical external-cavity surface-emitting laser array (VECSEL), and thelike.

The light emitter array 102 is shown at an angle theta 104. The lightsources 110 may be individually modulated. When beams produced by thelight sources 110 are scanned across a photosensitive medium, a swath ofscan lines in an image is formed; the swath having a height which isproportional to a vertical separation 114 between the most distant lightsources 110A and 110L. The light emitter array 102 may have more or lessthan twelve light sources, and a wider or narrower spacing 116 betweenadjacent light sources.

The angle theta 104 allows a vertical distance 112 between adjacentlight sources in a vertical direction to be less than the spacing 116between adjacent light sources. A light array 102 may be, for example, amonolithic laser array; and may have a spacing 116 between adjacentlight sources of about 100 microns. However, in an electrophotographicprinting system, it may be desirable to have a beam spacing in avertical direction 108 of much less than 100 microns, for example, 5microns. This beam spacing may be achieved by rotating the light emitterarray 102 at the angle theta 104 relative to the light emitter array's102 scan direction axis 106, such that the vertical distance 112 betweenadjacent light sources in the vertical direction 108 is less than thespacing 116 between adjacent light sources 110K and 110L, 110J and 110K,110I and 110J and the like. Correspondingly, the vertical separation 114between the most distant light sources 110A and 110L can be adjusted byrotating the light emitter array 102 by the angle theta 104.

FIG. 2 a illustrates a cross sectional diagram of a portion of anoptical system 200 according to an embodiment of an electrophotographicprinting system. FIG. 2 b is an expanded cross sectional view 280 of thelight emitter array 102 showing light sources 110A, 110B, and 110L.Although, light sources 110C through 110K are not shown in FIG. 2, theyare between light sources 110B and 110L as shown in FIG. 1. Adjacentlight sources, such as 110A and 110B are separated by a verticaldistance 112. The most distant light sources 110A and 110L are separatedby a vertical separation 114. The vertical separation of the mostdistant light sources 110A and 110L determines a vertical separation114′, 114″, 114′″ (See FIGS. 4,5, and 6) of spots in an image of themost distant light sources 110A and 110L.

In FIG. 2 a, light beams 202A, 202B, and 202L are emitted from lightsources 110A, 110B, and 110L respectively. Light beams 202A, 202B, and202L travel substantially in the optical axis direction 246. Light beams202 travel through a collimating element 204, which may be a lens.

Substantially collimated light beams 206 are directed to a first opticalelement 210 which is capable of redirecting an angle of the collimatedlight beams 206 to form redirected light beams 214. The first opticalelement 210 may be a prism, a diffraction grating, a Fresnel prism, acylinder lens, a gradient index plate, or another optical element.Substantially collimated light beams 206 are shown as an embodiment ofan electrophotographic printing system; however, it is not necessary tohave collimated light beams 206. Converging or diverging beams may alsobe used rather than substantially collimated light beams 206. The firstoptical element 210 which has a first surface 208 and a second surface212 is shown as a prism in an embodiment of an electrophotographicprinting system. However, this embodiment is not limited to a prism, asdescribed by the list of alternative optical elements 210 above.

The redirected light beams 214 travel to a second optical element 218which is capable of redirecting the light beams 214 again to form lightbeams 224. The second optical element 218 may also be a prism, adiffraction grating, a Fresnel prism, a cylinder lens, a gradient indexplate, or another optical element. The second optical element 218 isshown as a prism having a first surface 216 and a second surface 220.Nonetheless, the second optical element 218 is not limited to a prism.

It is not necessary that the first optical element 210 be the same typeas the second optical element 218. As an example, the first opticalelement 218 may be a diffraction grating and the second optical elementmay be a gradient index plate. One skilled in the art will appreciatethat other combinations are possible, and therefore, this example is notlimiting.

The second redirected light beams 224 pass through a cylinder lens 226to become light beams 228. The light beams 228 pass through an aperture230. The aperture 230 defines a cross-section of each beam 228 which haspassed through the cylindrical lens 226, and determines which rays fromeach light source 110A through 110L pass through the optical system.

The cylindrical lens 226 brings each incoming beam 224 to a line focusat a polygon surface 232 of a polygon 304 (See FIG. 3). Focusing eachbeam to a line at the polygon surface 232 reduces the effect of therotational dynamic instability of the polygon 304 on the printingsystem. Rotational dynamic instability may be called wobble. Focusingeach beam 228 to a line at the polygon surface 232 also reduces theeffect of errors in the facet of the polygon 304 on the printing systemas shown in FIG. 3.

Beams 234 reflect from the surface 232 of a polygon 304 (See FIG. 3).After reflecting from the surface 232 of the polygon 304, the beams 234pass through a first scan lens 236 and a second scan lens 238 whichconverges beams 240 to spots 262A, 262B, and 262L. The spots 262A, 262B,and 262L correspond to light beams 202A, 202B, and 202L and illuminate asurface 242 of a photosensitive medium 244. The illumination of thesurface 242 of the photosensitive medium 244 exposes the photosensitivemedium 244, thereby forming a latent image on the surface 242 of thephotosensitive medium 244. The latent image can be an electrostaticpotential difference on the surface 242 which will be developed andtransferred to media as described in reference to FIG. 14. Thephotosensitive medium 244 can be a photoconductor.

A vertical distance 112′ between adjacent spots 262A and 262B isproportional to the vertical distance 112 between adjacent light sources110A and 110B. A vertical separation 114′ between the most distant spots262A and 262L is proportional to the vertical separation 114 between themost distant light sources 110A and 110L.

Either the first optical element 210, or the second optical element 218,or combinations thereof may be rotated around an axis in the verticaldirection 108. As an example, the first optical element 210 may berotated about an axis 252 in the vertical direction which passes nearthe first optical element 210. The second optical element 218 may berotated about an axis 254 which passes near the second optical element218. Both the first optical element 210 and the second optical element218 may be rotated around a vertical axis 250 passing near the firstoptical element 210 and the second optical element 218. Either the firstoptical element 210, or the second optical element 218, or both may berotated around another vertical axis such as 328 which will be describedin reference to FIGS. 3 and 8.

It is not necessary that either the first optical element 210, or thesecond optical element 218, or both be precisely rotated around avertical axis, such as, but not limited to, vertical axes 108, 250, 252,254, or 328. The vertical separation 114′ of the most distant spots 262Aand 262L; and the vertical distance 112′ of adjacent spots 262A and 262Bcan be controlled by rotations about a vertical axis which aresignificantly tilted in the scan axis direction 106 as shown anddescribed in reference to FIG. 3.

FIG. 3 shows a perspective view of an optical system 300 according to anembodiment of an electrophotographic printing system. Light sources110A, 110B, and 110L are part of a light emitter array 102 (not shown,see FIGS. 1 and 2). The light sources 110A, 110B, and 110L may berotated at an angle theta 104 relative to the light emitter array 102scan axis direction 106 for the purpose of establishing a verticaldistance 112′ between spots 262A and 262B, and a vertical separation114′ between spots 262A and 262L. Spots 262A and 262L may illuminate asurface 242 of a photosensitive medium 244. Spots 262A through 262L aresubsequently referred to as spots 262. A small change in the angle theta104 can result in a relatively large change in both the verticaldistance 112′ and vertical separation 114′ between spots 262. Thissensitivity to the small change in angle theta 104 is undesirable foradjusting the vertical separation 114′ because a change in the angletheta 104 due to thermal shock, vibration, or other factors maysignificantly change both the vertical distance 112′ and verticalseparation 114′ between the spots 262. Such a change in both thevertical distance 112′ and vertical separation 114′ between spots 262can result in undesirable banding in a printed image.

In a similar manner as described in reference to FIG. 2, a light beam202B traveling in an optical axis direction 246 of the coordinate system310 passes through a collimating element 204. The collimating element204 may be a lens. For clarity, light beams 202A, and 202C through 202Lare not shown. Light beam 202B is represented by a single line. Thelight beam 202B passes through a first optical element 210 and a secondoptical element 218. The first optical element 210 and the secondoptical element 218 are configured to magnify anamorphically. Either thefirst optical element 210, or the second optical element 218 or bothelements may be adapted to magnify anamorphically. Anamorphicmagnification is characterized as having a different magnification in avertical direction 108 than in a scan axis direction 106.

After the light beam 202B passes through the first optical element 210and the second optical element 218, the light beam 202B is representedby reference number 202B′. The light beam 202B′ passes through acylindrical lens 226 to form a light beam 202B″. An aperture 230 definesthe cross-section of the beams 202A″ through 202L″ including the beam202B″, and determines which rays in the beams 202A″ through 202L″ passthrough the optical system 300.

Beam 202B″ is focused to a line on the polygon surface 232 of polygon304. Focusing light beams 202A′ through 202L′ (which include light beam202B′) to lines at the polygon 304 surface 232 reduces the effect of therotational dynamic instability of the polygon 304 on the printingsystem. Dynamic instability is sometimes called wobble. Focusing eachbeam 202A′ through 202L′ to a line at the polygon surface 232 alsoreduces the effect of errors in the facet of the polygon 304 on theprinting system. After beam 202B″ is reflected from the surface 232 of arotating 306 polygon 304, the stationary beam 202B″ is converted into ascanning beam 202B′″. The rotation 306 of the polygon 304 issubstantially around an axis in the vertical direction 108 and changesthe angular direction of the beam 202B′″ in time in the x′-z′ planedefined by the scan axis direction 106′ and the optical axis direction246′. Beam 202B′″ is illustrated at a time when the beam 202B′″ travelssubstantially along the primed optical axis direction 246′ in coordinatesystem 312.

Light beam 202B′″ passes through a first scan lens 236 and a second scanlens 238. The light beam 202B′″ which exits the second scan lens 238,renders a spot 262B on a surface 242 of a photosensitive medium 244. Thephotosensitive medium 244 may be flat or curved. The curvedphotosensitive medium 244 may include, but is not limited to a shape ofa cylinder. The photosensitive medium 244 may be a photoconductor. Spots262A and 262L are also shown on the surface 242 or the photosensitivemedium 244.

Spots 262A, 262B, and 262L are aligned at an angle theta prime 104′relative to the scan axis direction 106′, as defined by coordinatesystem 312. The scan axis direction 106′ is also referred to as the scandirection. Rotation 316 of the photosensitive medium 244 around an axissubstantially in the scan axis direction 106′ in combination withrotation 306 of the polygon 304 forms scan lines 410A, 410B, and 410L onthe photosensitive medium 244. The vertical distance 112′ betweenadjacent scan lines 410A and 410B varies with the angle theta 104 of thelight emitter array (See FIGS. 1 and 2). Light beams 202A″″ and 202L″″are shown and result from light sources 110A and 110L respectively.Light beams 202A″″ and 202L″″ may be overscaned beyond a print format inthe scan direction 106′ to illuminate scan lines 410A and 410L on asurface 336 of a first optical sensor 318.

A connection 320 communicates signals from the first optical sensor 318to a controller 322. The controller 322 processes information from thefirst optical sensor 318 to determine the vertical separation 114′between the light beams 202A″″ and 202L″″ and hence the verticalseparation between scan lines 410A and 410L.

The controller 322 compares the vertical separation 114′ with a desiredswath height value 334 which may be stored in a memory element in thecontroller, stored externally from the controller 322, or input to thecontroller from an external source. The controller 322 compares thevertical separation 114′ with the desired swath height value 334, andgenerates an error value 340 (See FIG. 14) in controller 322. A controlsignal 324 including electrical voltage or current signals, for example,an electrical signal 330 such as a pulse 331 or other types of signalsare formed from the error value 340. As an example, the pulse 331 canhave a pulse width 332 ranging from about 1 millisecond to 10 seconds.The pulse 331 is shown to be positive, even though pulse 331 can benegative and of various controllable amplitudes.

The control signal 324 drives an actuator 326. The actuator may includea coreless direct current motor operatively coupled to a cam. Theactuator may also include a gear reducer. One or more pulses 331, havinga 1 millisecond pulse width 332, may be used to move the actuator a verysmall and precise amount. A pulse 331 having a 10 second pulse width 332may be used to move the actuator 326 a full revolution or more.

The actuator 326 is operatively coupled to either the first opticalelement 210, the second optical element 218, or combinations thereof.The actuator 326 may rotate 308 either the first 210 or the second 218optical element or combinations thereof around a vertical axis 250. Thefirst optical element 210 may be rotated 308 around a vertical axis 252.The second optical element 218 may be rotated 308 around a vertical axis254. Either the first 210 or the second 218 optical elements, orcombinations thereof may be rotated 308 around a vertical axis 328 whichhas been displaced from vertical axes 250, 252, and 254. Furthermore,optical elements 210 or 218 or both may be rotated 308 around anyvertical axis, as shown by the vertical axis direction 108 in coordinatesystem 310. The optical elements 210 or 218 or both may be rotated 308to reduce the magnitude of the error value 340 as described in referenceto FIG. 14.

As will be shown and described in reference to FIG. 11, the actuator 326may also be configured to selectively rotate 338 either the firstoptical element 210 or the second optical element 218, or both the firstoptical element 210 and the second optical element 218 around an opticalaxis direction 246.

FIG. 4 shows swaths 402, 404, 406, and 408 which are correctly aligned400 according to an embodiment of an electrophotographic printingsystem. Light sources 110A through 110L form light beams 202A through202L (See FIGS. 1 and 2). Light beams 202A through 202L are scanned bypolygon 304 (See FIG. 3) and form a swath 402 which includes scan lines410A through 410L. Swath 402 is an example of an illumination patternwhich can be formed on a surface 242 of a photosensitive medium 244 asshown in FIGS. 2 and 3. The swath 402 may be developed with ink or tonerand transferred to media 1418 (See FIG. 14) to form a printed image. Inoperation, an electrophotographic printing system can modulate the beamsforming scan lines within swath 402 to form individual exposed areaswhich, after development, become printed areas such as pixels,subpixels, half-tone dots and the like. The individual exposed areas canbe arranged to render a printed image.

Swath 402 includes scan lines 410A through 410L. Adjacent scan lines 410are separated by the vertical distance 112′. The most distant scan lines410A and 410L are separated by the vertical separation 114′. A secondswath 404 is above the first swath 402, a third swath 406 is above thesecond swath 404, and a forth swath 408 is above the third swath 406. Agap 412 occurs between swaths 402 and 404, swaths 404 and 406, andswaths 406 and 408. If the height of the gap 412 between swaths issubstantially similar to the vertical distance 112′ between adjacentscan lines 410, then banding may not be apparent, or at least minimized.

The vertical distance 112′ and the vertical separation 114′ are in thevertical direction 108. The long dimension of swaths 402, 404, 406, and408; and scan lines 410A through 410L are in the scan axis direction106′.

FIG. 5 illustrates swaths 502, 504, 506, and 508, which are incorrectlyaligned 500. Scan lines 510A through 510L are spaced too far apartaccording to an embodiment of an electrophotographic printing system. Ina similar manner as described in FIG. 4, swaths 502, 504, 506, and 508each have a vertical distance 112″ between adjacent scan lines 510Athrough 510L. Scan lines 510A through 510L occur within a swath. Themost distant scan lines 510A and 510L are separated by a verticalseparation 114″. The vertical distance 112″ between adjacent scan lines510 within a swath is greater than a gap 512 which occurs between swaths502, 504, 506, and 508. This increased vertical distance 112″ may be aresult of angle theta 104 (See FIGS. 1 and 3) on the light emitter array102 (See FIG. 1) being large, causing the gap 512 to be less than thevertical distance 112″ between adjacent scan lines 510. The relativelysmall gaps 512 between swaths 502, 504, 506, and 508 visually appear asbanding. Two scan lines 510A and 510L on each side of the gap 512 appearas a dark band.

FIG. 6 illustrates swaths 602, 604, 606, and 608, which are incorrectlyaligned 600. Scan lines 610A through 610L are spaced too close togetheraccording to an embodiment of an electrophotographic printing system.

In a similar manner as described in FIG. 4, swaths 602, 604, 606, and608 each have a vertical distance 112′″ between adjacent scan lines 610Athrough 610L. The most distant scan lines 610A and 610L are separated bya vertical separation 114′″. The vertical distance 112′″ betweenadjacent scan lines 610 within a swath is narrower than a gap 612 whichoccurs between swaths 602, 604, 606, and 608. This relatively smallervertical distance 112′″ may be caused by too small of an angle theta 104(See FIG. 1) on the light emitter array 102, which in turn can cause thegap 612 to be wider than the vertical distance 112′″ between adjacentscan lines 610 within a swath. The relatively large gaps 612 between theswaths 602, 604, 606, and 608 visually appear as banding. Theanomalously wide gap 612 between the two scan lines 610A and 610Lappears as a light band.

FIG. 7 shows an optical sensor 318 illuminated with scan lines 410A and410L and a spatial exposure distribution profile 708 of sensed scanlines 410A and 410L according to an embodiment of an electrophotographicprinting system.

During configuration, alignment, or another procedure, scan lines 410Aand 410L may illuminate a first optical sensor 318 at an end of a scan(beyond an edge of a printed image area) as shown in FIGS. 3 and 7. Thefirst optical sensor 318 may also be at the beginning of the scan, suchas, before the start of the printed image area, or in any other positionin which the first optical sensor 318 may be illuminated. Non-scanningspots 262 (See FIG. 3) formed by light beams 202″″ may be positioned onthe first optical sensor 318, in combination with, or as a replacementfor, scan lines 410A and 410L. The scan lines 410A and 410L are formedby scanning spots 262. The vertical separation 114′ between, forexample, the most distant scan lines 410A and 410L can be sensed by thefirst optical sensor 318.

The first optical sensor 318 has a width 702 along the scan axisdirection 106′ and a height 704 along a vertical direction 108. Opticalsensor elements 706 may be arranged along the width 702 and height 704.The optical sensor 318 may be, but is not limited to, a charge coupleddevice, a CMOS device, a multi-element photodiode, a photosensitivemedium, a position sensitive device, or a split sensor.

The scan lines 410A and 410L form the spatial exposure distributionprofile 708 along a vertical direction 108 on the surface 336 of thefirst optical sensor 318. The spatial exposure distribution profile 708has a first peak 710 and a second peak 712 coincident with the exposureintensity of the first scan line 410A and the last scan line 410Lrespectively. Alternately, other scan lines could be used. The peaks 710and 712 may also represent a spatial distribution of the exposure ofnon-scanning spots 262 (See FIG. 3) on the first optical sensor 318. Thepeaks 710 and 712 may also represent the spatial exposure distributionprofile 708 of the exposure intensity of the scan lines 410A and 410Laveraged in the scan axis direction 106′. The distance 726 between thefirst 710 and second 712 peaks is an indicator of the verticalseparation 114′. Averaging, or other data processing in the scan axisdirection 106′ can reduce the variability of the measured distance 726between the first 710 and second 712 peaks and increase the accuracy ofthe measurement.

The distance 726 between the first 710 and second 712 peaks can becalculated by the difference between an estimate of the location of thesecond peak 724 and an estimate of the location of the first peak 718.An estimate of the location 718 of the first peak 710 may be obtained bymeasuring a first edge 714 of the first peak 710 and a second edge 716of the first peak 710, and by averaging the first edge 714 with thesecond edge 716, the edges being determined by the intersection of theexposure distribution 708 and a predetermined exposure level (notshown). Likewise, an estimate of the location 724 of the second peak 712can be obtained by measuring a first edge 720 of a second peak 712 and asecond edge 722 of the second peak 712 and averaging the first edge 720with the second edge 722. The location of the peaks 718 and 724 can alsobe estimated by a weighted average, the median, the mode, one half therange, the difference between the first edges 714 and 720, thedifference between second edges 716 and 722 or any other calculation ofthe distance between scan lines 410A and 410L. The calculations ofdistance 726 may use one or more of multiplication, division,subtraction, or addition, or combinations thereof.

FIG. 8 shows an embodiment of an adjustment mechanism 800 for rotating308 either a first optical element 210, or a second optical element 218,or combinations thereof around a vertical direction 108. The rotation308 is shown as counterclockwise, however it may also be clockwise. Allof the light beams 202A through 202L pass through the optical elements210 and 218, however, not all of the light beams are shown for clarity.One beam is shown for each of the illustrated beams 202A and 202L. Anyone of the optical elements 210 and 218 may be one or more of a prism, adiffraction grating, a Fresnel prism, a cylinder lens, or a gradientindex plate, or combinations thereof.

The optical elements 210 and 218 are rotated 816 around an axis 328 in avertical direction which may or may not be through the optical elements210 and 218. For example, the optical elements 210 and 218 may berotated 308 around a vertical direction 108 which is in the samedirection as the vertical direction 328. The rotation 308 around thevertical direction 108 may be displaced in the scan axis direction 106or the optical axis direction 246 or both.

The optical elements 210 or 218 or both may be rotated to reduce themagnitude of the error value 340 as discussed in reference to FIG. 14.

Optical elements 210 and 218 are operatively coupled to a movable mount802. A surface 818 on the movable mount 802 contacts a cam 810. The cam810 is coupled to a shaft 812 and may be offset from the shaft. Theshaft 812 is coupled to a motor 814. The motor 814 may be a corelessdirect current motor and may include a gear reducer (not shown). The cam810, the shaft, 812, and the motor 814 form an actuator 326. The surface818 of the movable mount 802 remains in contact with the cam 810 by aretainer 806 which may be a spring, a flexure, a flexible membrane, orany other force producing member. The retainer 806 is attached to afixed mount 808 which is relatively stationary with respect to themovable mount 802.

The motor 814 is driven by an electrical voltage or current signal. Forexample an electrical signal 330 including a pulse 331, the pulse 331having a width 332. A pulse width 332 of 10 seconds for pulse 331 maycause the cam 810 to rotate a complete revolution. A pulse width 332 of1 millisecond may cause the cam 810 to rotate a small and repeatableamount. Rotation 820 of the cam 810 results in rotation 816 of themovable mount 802 around: a pivot shaft 804, a flex pivot (not shown),or other rotatable bearing to effect rotation 816 of either opticalelement 210, or optical element 218, or both optical element 210 andoptical element 218 around an axis 328. The rotation 816 may beclockwise or counterclockwise.

Rotation 816 changes the paths of light beams 202A′ and 202L′ resultingin a changing vertical separation 114′ between the most distant spots262A and 262L on a surface 242 of a photosensitive medium 244.

Although rotations 308 have been described as rotating around an axis inthe vertical direction 108; off-axis deviations due to toleranceinaccuracies, desired optical configurations, or other factors arepossible. The rotation 308 about an axis in the vertical direction 108may also be substantially in the vertical direction, such as, within therange of 45 to 135 degrees from the scan axis direction 106. Also, thevertical direction 108 may be within a narrower range of about 80 to 100degrees from the scan axis direction 106.

FIG. 9 is a graph 900 of a scan line vertical position as a function ofan optical element rotation around a vertical axis according to anembodiment of an electrophotographic printing system. If the opticalelements 210 and 218 are prisms (See FIG. 8); and the prisms are rotated816 about a vertical axis 328, the change in a scan line verticalposition is shown as a function of prism rotation. The curve 910A showsthe change in the vertical position of scan line 410A (See FIG. 4) as apercentage of the nominal distance between scan lines 410A and 410L.Similarly, the curve 910L shows the change in the vertical position ofscan line 410L (See FIG. 4) as a percentage of the nominal distancebetween scan lines 410A and 410L.

FIG. 10 is a graph 1000 of the percentage change in the verticalseparation between two scan lines as a function of optical elementrotation around a vertical axis according to an embodiment of anelectrophotographic printing system. Curve 1002 shows the differencebetween curves 910L and 910A (See FIG. 9) as a percentage change in thevertical separation 114′ (See FIG. 4) between most distant scan lines410A and 410L. Curve 1002 is a function of optical element rotation 816(See FIG. 8) around a vertical axis 328. The slope of curve 1002 isrelatively low, which is a desirable property, in that the rotation 328(See FIG. 8) of the optical elements 210 and 218 effects a relativelysmall percentage change in the vertical separation 114′. Curve 1002 issubstantially linear over the shown range of rotation 816 (See FIG. 8)about a vertical direction 328. The property of linearity is useful in acontrol system, because linear relationships have well establishedtheories for stability and system performance.

FIG. 11 illustrates another embodiment of an adjustment mechanism 1100for rotating optical elements 210 and 218 (not shown in FIG. 11; howeverthe second optical element 218 is behind the first optical element 210in the optical axis direction 246 as shown in FIGS. 2, 3, and 8) around1114 an optical axis direction 246 according to an embodiment of anelectrophotographic printing system. The rotation 1114 is shown asclockwise, however it may also be counter clockwise. Light beams 202Aand 202L pass through the optical elements 210 and 218 (not shown). Notall of the light beams are shown for clarity and one ray, represented bya line is shown for each of the illustrated beams 202A and 202L. Any oneof the optical elements 210 and 218 may be one or more of a prism, adiffraction grating, a Fresnel prism, a cylinder lens, a gradient indexplate, or combinations thereof. Other optical elements 210 and 218 whichexhibit anamorphic magnification may be used.

As an example, the first optical element 210 may be a first cylinderlens having positive optical power in a y-z plane containing thevertical direction 108 and the optical axis direction 246. The secondoptical element 218 (See FIGS. 2, 3, and 8) is behind the first opticalelement 210 in the optical axis direction 246. The second opticalelement 218 may be a second cylinder lens having negative optical powerin a y-z plane containing the vertical direction 108 and the opticalaxis direction 246. In combination, the first and second cylinder lensesmay form an afocal cylindrical telescope having anamorphicmagnification. The afocal cylindrical telescope may have opticalmagnification in the vertical direction 108, but no magnification in thescan axis direction 106. Rotating either the first cylinder lens, thesecond cylinder lens, or combinations thereof about an optical axis 246effects a change in the vertical separation 114′ (See FIG. 4).

As previously mentioned, the first optical element 210 and the secondoptical element 218 (See FIGS. 2, 3, and 8) are rotated 1114 around theoptical axis direction 246. The optical elements 210 or 218 or both maybe rotated 1114 to reduce the magnitude of the error value 340 (See FIG.14). Optical elements 210 and 218 (See FIGS. 2, 3, and 8) areoperatively coupled to a rotary member 1106 having gear teeth 1108. Therotary member 1106 rotates in an opening 1104 within a housing 1102. Ahelical worm 1110 on a shaft 1112 is operatively coupled to the gearteeth 1108. The shaft 1112 is operatively coupled to a motor 814. Themotor 814 may be a coreless direct current motor and may include a gearreducer (not shown). A coreless direct current motor offers repeatablepositional control when driven with an electrical signal 330 having apulse 331 with a width 332, for example, of 1 millisecond. The rotarymember 1106, the shaft 1112, and the motor 814 form an actuator 326′.

The motor 814 is driven by electrical voltage or current signal, forexample, an electrical signal 330 having a pulse 331 with a width 332. Apulse width 332 of 10 seconds may cause the optical elements 210 and 218(See FIGS. 2,3, and 8) to rotate a complete revolution. A pulse width332 of 1 millisecond may cause the optical elements 210 and 218 (notshown) to rotate a small and repeatable amount. The pulse 331 may bepositive or negative.

When the first optical element 210 and the second optical element 218(See FIGS. 2, 3, and 8) are rotated 1114, the angle of beams 202A and202L change. The changing angle of beams 202A′ and 202L′ varies thevertical separation 114′ of the spots 262A and 262L on the surface 242of the photosensitive medium 244. The varying vertical separation 114′changes the height of swaths 402, 404, 406, and 408 (See FIG. 4). As anexample, the vertical separation 114″ (See FIG. 5) of swaths 502, 504,506, and 508 may be adjusted to a desired swath height value 334 (SeeFIGS. 3 and 14) to match the vertical separation 114′ (See FIG. 4).Therefore, the height of the swaths 502, 504, 506, and 508 (See FIG. 5)may be adjusted by rotating 1114 the first optical element 210 and thesecond optical element 218 (See FIGS. 2, 3, and 8) around the opticalaxis direction 246 to match the vertical separation 114′.

It is not necessary to vary both of the optical elements 210 and 218.The first optical element 210 or the second optical element 218 may bevaried independently to achieve a similar effect.

Furthermore, the first optical element 210, the second optical element218 (See FIGS. 2, 3, and 8), or both the first optical element 210 andthe second optical element 218 may be rotated 1118 around an axis 1116.The axis 1116 is in the y-z plane as defined by the vertical direction108 and the optical axis direction 246. The variation in verticalseparation 114′ (See FIG. 4) by rotation 1118 about the axis 1116 can beexpected to produce a curve intermediate to the curves 1002 (See FIG.10) and 1302 (See FIG. 13) respectively. Although rotations 1118 havebeen described as rotating 1118 around an axis 1116 in the y-z plane;off-axis deviations due to tolerance inaccuracies and desired opticalconfigurations are possible. The axis 1116 may deviate from the y-zplane defined by a vertical direction 108 and an optical axis direction246 from about 80 to 100 degrees in the scan axis direction 106.

FIG. 12 is a graph 1200 of scan line vertical separation as a functionof optical element rotation about an optical axis direction according toan embodiment of an electrophotographic printing system. If the opticalelements 210 and 218 are prisms (See FIG. 11); and the prisms arerotated 1114 about an optical axis direction 246, a change in scan linevertical position is shown as a function of prism rotation 1114 in FIG.12. Curve 1202A shows the change in a vertical position of scan line410A as a percentage of the nominal distance between scan lines 410A and410L. Similarly, curve 1202L shows the change in the vertical positionof scan line 410L as a percentage of the nominal distance between scanlines 410A and 410L.

FIG. 13 is a graph 1300 of the percent change in the vertical distancebetween two scan lines as a function of optical element rotation aroundan optical axis according to an embodiment of an electrophotographicprinting system. Curve 1302 shows the difference between curves 1202Land 1202A (See FIG. 12) and represents the percentage change in verticalseparation 114′ (See FIG. 4) of scan lines 410 as a function of opticalelement rotation 1114 (See FIG. 11) about an optical axis direction 246.Curve 1302 is substantially linear over the shown range of rotation 1114(See FIG. 11) around the optical axis direction 246. The slope of curve1302 represents the sensitivity of the change in the vertical separation114′ (See FIG. 4) to the change in rotation 1114 (See FIG. 11). Althoughthis sensitivity is greater than for the rotation 816 (See FIG. 8) ofthe optical elements 210 and 218 around an axis in the verticaldirection, it is less sensitive than for the change in the angle theta104 (See FIG. 1) of the light emitter array 102. This lower sensitivityis useful, since the rotation 1114 (See FIG. 11) of the optical elements210 and 218 effects a relatively small change in the vertical separation114′ (See FIG. 4), as compared with changes to the angle theta 104 (SeeFIG. 1) of the light emitter array 102. Curve 1302 is substantiallylinear, making it useful and predictable in a control system, becauselinear relationships have well established theories for stability andsystem performance.

FIG. 14 illustrates a system diagram of an electrophotographic printingsystem 1400 according to an embodiment of an electrophotographicprinting system. The methodology of the image formation using theelectrophotographic printing system 1400 can be accomplished using drypowder toner or liquid ink (also known as liquid toner) systems, forexample, the HP INDIGO® Press 5000, available from Hewlett-Packard.

In an embodiment of an electrophotographic printing system, the surface242 of a photosensitive medium 244 is electrified by a corotron,scorotron, charge roller or another charger 1404. A light beam or lightbeams 202 from a light emitter array 102 are incident on the surface 242of the photosensitive medium 244 and form a latent electrostaticallycharged image thereon. An ink delivery system 1408 is a dispenser ofink, toner, or another type of colorant. The ink or toner may be aliquid or a powder. The ink delivery system may be a binary inkdeveloper BID. Multiple BID cartridges may be used, each containing adifferent color ink or toner. The latent image is developed by the inkor toner to form a visible image on the surface 242 of thephotosensitive medium 244. In some embodiments of theelectrophotographic printing system 1400, a squeegee roller 1412compresses the image and removes excess liquid therefrom. The image istransferred to an intermediate transfer member ITM 1414. The image isthen transferred to a medium 1418 at a nip between the ITM 1414 and animpression roller 1416. After transfer of the image to the ITM 1414,residual toner and charge on the photosensitive medium 244 may beremoved by a cleaning apparatus 1420, which may be an electricaldischarge and a wiper.

Controller 322 is programmed with software to, among other thingscontrol the light emitter array 102 to write latent images. Controller322 also receives data pertaining to vertical separation 114′ (See FIG.3) and makes corrections to the electrophotographic printing system 1400for correctly adjusting the vertical separation 114′. For example, thevertical separation 114′ can be adjusted by directing the actuator 326to alter a latent image on the surface 242 of a photosensitive medium244 by rotating either a first optical element 210 a second opticalelement 218 (not shown. See FIGS. 2, 3, and 8) or both.

The adjustment of the vertical separation 114′ may be accomplishedautomatically, or semi-automatically. In an embodiment of theelectrophotographic printing system 1400 where the adjustment of thevertical separation 114′ is adjusted semiautomatically, data may beprovided to the controller 322 through an input device 1426. The inputdevice 1426, for example, may include a keyboard, mouse, or another typeof device. The mouse may select adjustment options from a menu. Dataprovided to the controller 322 by input device 1426 may result frominspections or measurements from a test pattern which has been printedon a medium 1418 by the electrophotographic printing system 1400. Thevertical separation 114 (See FIGS. 2, 3, 4 and 8) may be adjusted byrotating a first optical element 210, a second optical element 218 (SeeFIGS. 2, 3 and 8) or both. The first optical element 210 may be rotatedby an actuator 326 operatively coupled by a control signal 324 to acontroller 322. The rotation of the first optical element 210, thesecond optical element 218 (See FIGS. 2, 3 and 8) or both can change thevertical separation 114′ (See FIGS. 3 and 4) on the printed media 1418.The vertical separation 114′ can be measured from the printed media 1418and entered into the input device 1426 which rotates the optical elementto change the vertical separation 114′. This process can be continueduntil an acceptable vertical separation 114′ is printed on the media1418.

In some embodiments of the electrophotographic printing system, thevertical separation 114′ (See FIGS. 3 and 4) may be adjustedautomatically by a controller 322 using a first sensor 318 in operativecommunication with the controller 322. The first sensor 318 may detectone or more indicators of vertical separation 114′. The first sensor 318measures the swath height from light beams 202A″″ and 202L″″ (See FIG.3) or scan lines 410A and 410L (See FIGS. 3 and 7). The first sensor 318may also measure other beams or combinations of beams. The first sensor318 can be located near an edge of the photosensitive medium 244 (SeeFIG. 3) or in the conjugate location formed by a folding mirror (notshown) to a near-edge point of the photosensitive medium 244 so that thefirst sensor 318 does not block the formation of the latent image on thesurface 242 of the photosensitive medium 244.

The measured vertical separation 114′ (See FIGS. 3 and 4) is compared toa desired swath height value 334 to form an error value 340. If thevertical separation 114′ equals the desired swath height value 334, thenthe error value 340 is zero, and no adjustment of either the firstoptical elements 210 or the second optical element 218 (See FIGS. 3 and4) or both occurs. If the vertical separation 114′ is greater or lessthan the desired swath height value 334, then the error value 340 is notzero and either the first optical element 210 and the second opticalelement 218 (See FIGS. 2, 3, 4, and 8) or both are rotated to adjust thevertical separation 114′ (See FIGS. 3 and 4) to reduce the magnitude ofthe error value 340.

The optical elements 210 and 218 can be rotated by an actuator 326operatively coupled to the controller 322 by a control signal 324. Thecontroller 322 controls the actuator 326 by sending one or moreelectrical signals 330 having a pulse 331 with a width 332 to theactuator 326 by control signal 324. The controller 322 can command theelectrophotographic printing system 1400 to change the verticalseparation 114′ (see FIGS. 3 and 4) to match a desired swath heightvalue 334. The desired swath height value 334 may be communicated to thecontroller 322 through a hardware port, by an input device 1426, by inan internal register within the controller 322, and the like.

In other embodiments of the electrophotographic printing system 1400,the vertical separation 114′ (see FIGS. 3 and 4) may be adjustedautomatically by the controller 322 using a second sensor 1424 inoperative communication with controller 322. The second sensor 1424detects a printed pattern on the media 1418 and operatively communicateswith the controller 322 to adjust the first optical element 210, thesecond optical element 218 (not shown. See FIGS. 2, 3 and 8), or both byactuator 326 in a similar manner as described in the previousparagraphs.

FIG. 15 shows a flow diagram having procedural acts according to anembodiment of an electrophotographic printing system.

In act 1502, at least two spots 262 (See FIGS. 2, 3, 8, and 11) areformed on a surface 242 of a photosensitive medium 244. The at least twospots 262 can be used to form an electrostatic latent image on thesurface 242 of the photosensitive medium 244. The electrostatic latentimage on the surface 242 of the photosensitive medium 244 can bedeveloped with toner or ink to produce a printed image on media 1418 asshown in FIG. 14. The at least two spots 262 may be scanned by rotatinga polygon 304 (See FIG. 3) to form an electrostatic latent image andprinted swath 402, 404, 406 or 408 (See FIG. 4) with two or more scanlines 410. The printed density of the scan lines 410 may be modulated torender an image (not shown). One form of modulation is to alternatelyturn on and off a light source 110 (See FIG. 1) for printing alternatedark and light areas.

In act 1504, a vertical distance between at least two spots 262 (SeeFIGS. 2 and 3) can be obtained by the vertical separation 114′ betweenmost distant spots 262A and 262L, or the vertical distance 112′ betweenadjacent spots 262. A vertical distance may be obtained between anyspots 262 even if they are not the most distant or adjacent.

As an example, according to an embodiment of an electrophotographicprinting system, the vertical distance, and hence the verticalseparation 114′ (See FIG. 3), between most distant spots 262A and 262Lmay be obtained by a first optical sensor 318. Spots 262A and 262L arescanned by rotating 306 polygon 304 to form scan lines 410A and 410Lrespectively (See FIGS. 3 and 7). The scan lines 410A and 410L areseparated by substantially the same vertical separation 114′ as spots262A and 262L. According to an embodiment of an electrophotographicprinting system, the distance between the spots 262A and 262L can beobtained by detecting the scan lines 410A and 410L on a first opticalsensor 318 as shown and described in reference to FIGS. 3, 7, and 14.The separation between spots 262 may also be obtained by printing spots262, scan lines 410, or other objects, on a medium 1418 (See FIG. 14)and detecting the vertical distance between the spots 262, the scanlines 410, or the other objects using a second sensor 1424. The secondsensor 1424 may be an optical sensor similar to the first optical sensor318 as shown and described in reference to FIGS. 3, 7, and 14. Thesecond sensor may have a lens to reimage the printed medium onto thesensor.

The distance between the spots 262A and 262L can also be obtained byprinting spots 262, scan lines 410, or other objects, on a media 1418and measuring the vertical distance between the spots 262, the scanlines 410, or the other objects using a measuring device such as ascale, an optical comparator, a microscope, calipers, a scanner device(flatbed or other type) and the like.

In act 1506, an error value 340 (See FIG. 14) is formed by comparing theobtained vertical distance, for example, 114′ (See FIGS. 3 and 4) in act1504 to a desired swath height value 334 (See FIG. 14). The comparisonmay be made by a controller 322 (See FIGS. 3 and 14). The desired swathheight value 334 (See FIGS. 3 and 14) is shown external to thecontroller, although it can be internal to the controller such as datain memory.

In act 1508, a vertical distance 112′ (See FIGS. 2, 3, and 8), orvertical separation 114′ between at least two spots 262 may be adjustedby selectively rotating 308 one or more optical elements 210 or 218about a vertical direction 108, 250, 252, 254, 328. The optical elements210 and 218 may be prisms. Rotation 308 of one or more of the opticalelements 210 or 218 or both may be performed by an adjustment mechanism800 as shown in FIG. 8.

In act 1510, a vertical distance between at least two spots 262 (SeeFIG. 11) may be adjusted by selectively rotating one or more opticalelements 210 or 218 (See FIGS. 2, 3, and 8) or both around 1114 (SeeFIG. 11) an optical axis direction 246. The optical elements may beprisms. Rotation 1114 of one or more of the optical elements 210 or 218(See FIGS. 2, 3, and 8) or both may be performed by an adjustmentmechanism 1100 as shown in FIG. 11.

In act 1512, a vertical distance between at least two spots 262 (SeeFIG. 11) may be adjusted by selectively rotating 1118 one or moreoptical elements 210 or 218 (See FIGS. 2, 3 and 8) or both around anaxis direction 1116 (See FIG. 11) which is in the y-z plane of thevertical direction 108 axis and the optical axis 246. The opticalelements may be prisms. Rotation 1118 of one or more of the opticalelements 210 or 218 (See FIGS. 2, 3, and 8) or both may be performed byan adjustment mechanism 1100 in FIG. 11 which may be tilted at an angle(not shown) between the vertical direction 108 and an optical axisdirection 246.

An embodiment of an electrostatic printing system has been used todescribe how optical elements 210, 218 (See FIGS. 2, 3, 8, and 11) canbe rotated around an axis in the vertical direction 108, around an axisin the optical axis direction 246, around an axis in the y-z planeformed by the vertical direction 108 and the optical axis direction 246,or around combinations of axes thereof to adjust a vertical separation114′ or a vertical distance 112′ between spots 262 or scan lines 410(See FIG. 4). However, it is not necessary that the axis or axes be 90degrees from the scan axis direction 106. Substantial angular deviationsof the axes, in the range of 45 degrees to 135 degrees from the scanaxis direction 106 are acceptable. Deviations in the range of 80 to 100degrees can be achieved with current optical configurations.

While the present embodiments of an electrostatic printing system havebeen particularly shown and described, those skilled in the art willunderstand that many variations may be made therein without departingfrom the spirit and scope of the embodiments defined in the followingclaims. The description of the embodiment is understood to include allnovel and non-obvious combinations of elements described herein, andclaims may be presented in this or a later application to any novel andnon-obvious combination of these elements. The foregoing embodiments areillustrative, and no single feature or element would have to be includedin all possible combinations that may be claimed in this or a laterapplication. Where the claims recite “a” or “a first” element of theequivalent thereof, such claims should be understood to includeincorporation of one or more such elements, neither specificallyincluding nor excluding two or more such elements. Although exemplaryembodiments of an electrophotographic printing system have beendescribed, the application is not limited and may include a photocopier,a facsimile machine, a photographic output scanner, analyticalequipment, and the like.

What is claimed is:
 1. An apparatus comprising: a light source operableto produce a linear array of two or more concurrent light beams inrespective parallel beam directions; an optical element having anoptical axis parallel to the beam directions and configured toanamorphically magnify the light beams with different magnification in avertical direction relative to a direction along a second axissubstantially in a plane formed by the vertical direction and theoptical axis; an adjustment mechanism coupled to the optical element toselectively rotate the optical element either around an axissubstantially in the vertical direction, the optical axis, the secondaxis, or combinations of axes thereof to adjust vertical separationbetween two or more spots respectively formed on a surface by the two ormore light beams after being anamorphically magnified by the opticalelement; an optical sensor to capture images of the two or more spotsformed on the surface; and a controller to determine a verticalseparation between the two or more light beams based on the capturedimages and to control the adjustment mechanism to adjust the verticalseparation between the two or more spots formed on the surface based onthe determined vertical separation.
 2. The apparatus in claim 1, whereinthe optical element selectively rotates around either an axis in thevertical direction, an axis in the optical axis direction, or an axis inthe plane of an axis in the vertical direction and an axis in theoptical axis direction, wherein the axis is at an angle of about 80 to100 degrees with respect to a scan axis direction.
 3. The apparatus inclaim 1, wherein the optical element is one or more of a prism, aFresnel prism, a cylinder lens, a diffraction grating, or a gradientindex plate, or combinations thereof.
 4. The apparatus in claim 1,wherein the adjustment mechanism comprises an actuator.
 5. The apparatusin claim 4, wherein the actuator is a piezoelectric actuator, anelectromechanical actuator, or a mechanical actuator, or combinationsthereof.
 6. The apparatus in claim 4, wherein the actuator is anelectromechanical actuator comprising an electric motor.
 7. Theapparatus in claim 6, wherein the electric motor is a coreless directcurrent motor.
 8. The apparatus in claim 4, wherein the actuatorreceives at least one electrical signal from a controller, theelectrical signal characterized by at least one pulse having a widthfrom about 1 millisecond to 10 seconds.
 9. The apparatus in claim 8,wherein the controller receives a signal from an optical sensor, or aninput device, or combinations thereof.
 10. The apparatus in claim 8,wherein the controller receives a signal from an optical sensor and thesignal is substantially linear with rotation of the optical element. 11.The apparatus in claim 1, further comprising a controller operable toscan the spots over the surface to form respective scan lines across thesurface.
 12. The apparatus in claim 11, wherein the surface isphotosensitive.
 13. The apparatus in claim 12, wherein the surface iscylindrical.
 14. The apparatus in claim 1, wherein the spots are on anoptical sensor surface.
 15. An apparatus comprising: a light sourceoperable to produce a linear array of two or more concurrent light beamsin respective parallel beam directions; a first optical element having afirst and a second surface; a second optical element having a first anda second surface; wherein the first surface of the second opticalelement is facing and spaced apart from the second surface of the firstoptical element to form a gap therebetween and wherein the first opticalelement, or the second optical element, or both the first opticalelement and the second optical element in combination are configured toanamorphically magnify the light beams with different magnification in avertical direction relative to a direction along a second axissubstantially in a plane formed by the vertical direction and an opticalaxis; an actuator coupled to the first and second optical elements andoperable to selectively rotate either the first optical element or thesecond optical element, or combinations thereof around either an axissubstantially in the vertical direction, the optical axis, the secondaxis, or combinations of axes thereof, to adjust vertical separationbetween two or more spots respectively formed on a surface by the two ormore light beams after being anamorphically magnified by the opticalelement; an optical sensor to capture images of the two or more spotsformed on the surface; and a controller to determine a verticalseparation between the two or more light beams based on the capturedimages and to control the actuator to adjust the vertical separationbetween the two or more spots formed on the surface based on thedetermined vertical separation.